1. Field of the Invention
The present invention relates to refrigeration systems and more particularly relates to compressor-condenser-evaporator type refrigeration systems wherein the compressor is cyclically operated.
Refrigeration systems of the sort generally employed in household refrigerators, chillers and coolers of various descriptions include a positive displacement refrigerant compressor, a refrigerant condenser and a refrigerant evaporator to which refrigerant flows from the condenser via an expansion device which restricts the refrigerant flow. High pressure gaseous refrigerant is discharged from the compressor into the condenser where heat is transferred from the refrigerant resulting in its liquification at high pressure. The refrigerant passes through the expansion device and returns to its gaseous state in the evaporator, absorbing heat from the surroundings of the evaporator in the process and resulting in the evaporator producing a cooling effect. Low pressure gaseous refrigerant is returned to the compressor intake from the evaporator.
The compressor is typically cycled on and off in response to the sensed temperature of a medium (air, water, etc.) cooled by the evaporator. When a desired low temperature level is sensed the compressor is cycled off so that the flow of high pressure gaseous refrigerant from the compressor is terminated; but the refrigerant already delivered to the condenser continues to condense and flow to the evaporator through the expansion device until the pressures in the condenser and evaporator equalize or until the compressor is cycled on again. This results in an unnecessary additional cooling effect beyond the desired temperature level and, more importantly, requires the compressor to pump the condenser back up to operating pressure each time the compressor is cycled on. In applications such as household refrigerators it has been estimated that approximately seven percent of the energy consumption of the appliance is attributable to the operation of the compressor in restoring the condenser pressure.
2. The Prior Art
In order to reduce that portion of refrigeration system energy consumption attributable to restoring the condenser pressure when the compressor is cycled on, it has been proposed that an electrically actuated refrigerant valve be placed in the refrigeration system between the condenser and evaporator. The proposed valves are operated by a solenoid which is energized to close the valve and deenergized to open the valve. Whenever the compressor is operating the solenoid is deenergized so that refrigerant flows normally through the system. When the compressor cycles off, the solenoid is energized, closing the valve and blocking flow of refrigerant from the condenser. Thus the condenser remains at an elevated pressure during periods when the compressor is inactive because refrigerant flow from it is blocked.
When the compressor is energized again the refrigerant valve reopens so that the refrigeration system immediately begins operating at close to its optimal performance level.
The refrigerant control valve operation has some drawbacks including the fact that the valve actuating solenoid is energized while the compressor is deenergized. This energization represents an additional source of system power consumption thus reducing the energy saving effect of the valve. Furthermore, solenoids can create operating noises which are disconcerting to system users because the noise occurs when the system is otherwise deactivated.
While it is possible to construct such a refrigerant valve so that the solenoid is energized to open the valve and therefore is energized only when the compressor operates, failure of the solenoid in such circumstances would result in blockage of refrigerant flow through the system when the compressor is energized. This type of failure could damage the system.